Electroexplosive primer ignition assembly

ABSTRACT

An electrically actuated primer ignition assembly displaying a 0.75 ampere &#39;&#39;&#39;&#39;no fire&#39;&#39;&#39;&#39; characteristic for 60 seconds, and a 2.5 amperes &#39;&#39;&#39;&#39;all fire&#39;&#39;&#39;&#39; within 10 milliseconds after initial application of current, the &#39;&#39;&#39;&#39;all fire&#39;&#39;&#39;&#39; performance being maintained even after the &#39;&#39;&#39;&#39;no fire&#39;&#39;&#39;&#39; preconditionaining.

United States Patent 72] Inventor Cha Hubbard 3,062,146 11/1962 Williamset al. 102 46 Madisflllylll- 3,196,041 7/1965 McNulty et al. 102/28 [21]AppLNo. 740,298 3,227,083 l/1966 Moseset al. 102/28 [22] Filed June26,1968 3,291,046 12/1966 Dahl 102/28 [45] Patent d Jan. 26, 19713,450,045 6/1969 Zedalis 102/28 [73] Asslgnee Olm Comm-anon PrimaryExaminer verlin R. Pendegrass a corporation 0 Attorneys-Donald R.Motsko, H. Samuel Kieser, William W.

' Jones, Richard S. Strickler, Robert H. Bachman and 54 ELECTROEXPLOSIVEPRIMER IGNITION Thomas y ASSEMBLY 13 Claims, 2 Drawing Figs.

[52] U.S.Cl 102/28 51 Int. Cl F42b3/l2 Field ABSTRACT: An electricallyactuated primer ignition as- 149/2143 45 sembly displaying a 0.75 ampereno fire characteristic for References C ed 60 seconds, and a 2.5 amperesall fire within 10 milliseconds after initial application of current,the all fire per- UNITED STATES PATENTS formance being maintained evenafter the no fire precondi- 3,019,732 2/1962 Kaspaul 102/28 tioning.

PATENTEUJANZGISTI 3557.699

INVENTOR CHARLES L. HUBBARD ATTORNEY ELECTROEXPLOSIVE PRIMER IGNITIONASSEMBLY This invention relates to an electrically actuated primerassembly for use with an ejection-type cartridge of, for example, theStorz variety. The primer assembly of this invention exhibits a no firecharacteristic when subjected to a current of a least 0.75 amperes for aperiod of at least 60 seconds, and further exhibits an all firecharacteristic when subjected to a current of only 2.5 amperes whichoccurs within a period of less than milliseconds. The term no fire, asused in this disclosure, means that no ignition of the primer occurs,and the term "all fire," as used in this disclosure, means thatsubstantially all of the primer is ignited.

It is known in the prior art to provide a cartridge in which apropellant charge is disposed, which propellant charge is utilized toperform some work function. Such cartridges are found, for example, inmilitary aircraft and are used to eject the pilot from a crippled plane.Cartridges of this type are generally ignited by a separate primercharge which is associated with the propellant charge. Electricalignition assemblies are commonly provided for use in conjunction withthe primer charge, so that the primer charge is electrically ignited tofire the cartridge.

It is readily apparent that assemblies of this type are often one shotaffairs which may never be used, but which must be ready for use at alltimes since a man's life may dependon their reliability. It is thusimperative that such assemblies be made susceptible to periodic qualitycontrol testing in order to determine their operativeness under allconditions. Ideally, the testing should be capable of being carried outwithout requiring dismantling of the assembly. Furthermore, the assemblyshould be capable of being quickly tested under even the most adverse ofconditions. One of the most difficult portions of the assembly to testisthe electrical circuitry. Ideally, the circuits should be tested bypassing an electric current through them, however, since the primer iselectrically ignited, one faces the possibility of accidentally ignitingthe cartridge when thus testing the circuits. Furthermore, in order toreliably test the circuits, a current sufficient to be unaffected bycircuit resistance, limits in testing apparatus sensitivity, and thelike, must be passed through the circuit. This minimum current has, inthe past, been often sufficient to ignite the cartridge during testing.lt would be possible to lower the resistance in the circuit to such adegree that a minimum current passing therethrough would not be capableof accidentally igniting the cartridge, but such a step would thenadversely affect the firing capabilities of the assembly. Assemblies ofthis type must ideally be capable of utilizing a comparatively smallcurrent to produce an all fire of the primer within a comparativelybrief time period. In order to meet the latter requirement, theresistance of the ignition circuitry should be relatively high.

While in operation, all electrical circuits contained in an aircrafthave a continual flow of current, which flow has been termed straycurrent." The magnitude of stray current can be as high as 0.3 to 0.5amperes, and thus can present accidental ignition problems with respectto electrical ignition assemblies of the character described.

From the foregoing, it is apparent that an ideal ignition assemblyshould be capable of being subjected to a comparatively large amperagewithout igniting, and also should be capable of complete ignition uponthe application of a comparatively small amperage. This invention isdirected toward an ignition assembly for use with an ejection-typecartridge, which igni-.

tion assembly is electrically actuated. The ignition assembly of thisinvention can be subjected to a current of at least 0.75 ampere for aperiod of at least 60 seconds without firing. The application of thiscurrent can thus safely be used to test the circuitry in the ignitionassembly. The ignition assembly of this invention, furthermore, willfire in a period of less than about 10 milliseconds when subjected to acurrent of 2.5 amperes or more. lt is thus readily apparent that theignition assembly of this invention exhibits superior no fire testingcharacteristics along with excellent all fire characteristics;

Broadly, the ignition assembly of this invention includes: an electrodethrough which current is fed into the assembly; a ground; meansinterconnecting the electrode and ground, such as a bridge wire; a heatsink of electrical insulating material contacting the interconnectingmeans; and, when loaded, a charge of primer material adjacent to theinterconnecting means and in intimate contact therewith.

More particularly, the ignition assembly of this invention may includean electrically conducting housing member which is electrically groundedand which has a lining of electrical insulating material. An electrodeis disposed in the housing and separated therefrom by the insulatingliner. A ground member is disposed in the housing and electricallyconnected thereto, the ground defining a wall of a chamber into whichthe primer material is packed. A bridge wire is electrically connectedto the electrode and to the ground, the bridge wire extending across thebottom of the primer chamber so as to be in contact with the primingcharge when the latter is packed into the chamber. The bridge wire ismade of a metal which increases its resistivity as its temperature isincreased, thereby providing the heat necessary to ignite the primercharge. A heat sink is disposed in the housing. The heat sink definesthe bottom wall of the primer chamber and is in heat exchange contactwith the bridge wire. The heat sink underlies the bridge wire and isoperative to absorb and conduct heat away from the bridge wire. The heatsink thus contributes to the no fire" charac teristic of the ignitionassembly when circuit-testing amperage is applied thereto.

It is, therefore, an object of this invention to provide an electricallyoperated primer-ignition assembly of compact construction for use withejection-type cartridges and the like.

It is a further object of this invention to provide an ignition assemblyof the character described which will not fire when energized with acurrent of at least 0.75 amperes for a time period of at least 60seconds.

It is yet another object of this invention to provide an ignitionassembly of the character described which-will completely fire in a timeperiod of not more than about 10 milliseconds when energized with acurrent of about 2.5 amperes.

vIt is a still further object of this invention to provide an ignitionassembly of the character described which will retain its all firecharacteristic even after exposure to the no fire condition.

Other features, objects, and advantages of this invention will becomeapparent to those skilled in the art from the following description whenread in conjunction with the accompanying drawings, in which:

FIG. 1 is an exploded view of a preferred embodiment of an ignitionassembly formed in accordance with this invention; and

FIG. 2 is a side sectional view of the assembly of FIG. 1

Referring now to FIG. 1, the ignition assembly of this inventionpreferably includes a cup-shaped metallic housing member 2 which iselectrically grounded and in which is disposed a lining 4 of electricalinsulating material. An electrode 6 is mounted in the liner 4, theelectrode 6 preferably including an elongated stem portion 8 forconnection with a source (not shown) of electrical current, and anenlarged head portion 10 A post 12 is disposed on the head portion 10,the post 12 projecting through an aperture 14 in a heat sink body 16adjacent to the electrode head 10. An annular body 18 is mounted in thehousing 2 in electrical contact therewith, the body 18 being composed ofan electrically conducting material. A bridge wire 20 is disposedbetween the body 18 and the electrode post 12 to electricallyinterconnect the latter two. The bridge wire 20 is preferably welded tothe body 18 and to the electrode post 12. Furthermore, the bridge wire20 is disposed in contact 'with the heat sink 16 along substantially theentire length of the bridge wire. Thus, an electrical circuit isestablished between the electrode 6, the bridge wire 20, the annularbody 18, and the housing 2, the latter of which is electricallygrounded. i

FIG. 2 shows the assembled ignition assembly, and it is noted that theinner wall of the annular element or ground 18 forms the sidewall of aprimer chamber 22. The heat sink 16 forms the bottom wall of the primerchamber 22 and the bridge wire 20 extends across the bottom wall. Acharge of primer material 24 is packed into the primer chamber 22. Forfiring or testing, the electrode stem 8 is connected to a power source(not shown), the housing 2 is grounded, and the primer charge 24 ispositioned next to a body of propellant (not shown) to be ignited by theassembly.

With reference now to the specifics of the ignition assembly of thisinvention, the bridge wire is preferably formed from Nichrome alloy,with the physical embodiment of the bridge wire being controlled so asto provide a total unit resistance in the range of about 1.2-2.0 ohms.While Nichrome is the preferred bridge wire material, other materialshaving a temperature coefficient of resistivity approximately equal toabout .0004 ohm-cm. at 20 C. could be used in place of Nichrome.

The heat sink is preferably formed from Alumina. The heat sink may alsobe formed from a precast machined body of thermosetting epoxy resin, orfrom a mineral filled thermosetting epoxy resin, or from a pottedthermosetting epoxy resin. The heat sink must be formed from anelectrical nonconductor and should have a thermal conductivity in therange of about .002 to .040*. The heat sink should also have an adequatetemperature stability at about 300 C. for time durations of 60 secondsto prevent excessive melt.

The primer composition is formed from a homogeneous mixture of about 18percent to about 30 percent powdered zirconium, about 14 percent toabout 26 percent antimony sulfide, and from about 5 percent to about 70percent barium nitrate. The primer mixture is preferably granulated topass through a 325 mesh and is compacted into the primer chamber with acompaction pressure of greater than 6,000 psi. The preferred range ofcompaction pressures is from 8,000-l2,000 p.s.i. While the preferredgranulation of the primer mixture is such as will pass througha'325-mesh screen, one may use a more coarsely granulated mixturewithout departing from the spirit of this invention. The coarsening ofthe primer will not adversely affect the no fire and all firecharacteristics of the assembly of this invention, but will merely varythe burning properties of the primer.

Several variations of the ignition assembly of this invention weretested for no fire and all fire characteristics, using different ramcalories centimeter thickness Units of (centiilieter) seconds degrees 0heat sink materials. The tested assemblies all had bridge wires ofNichrome with a unit resistance in the 1.2 ohm to 2.0 ohm range, andwere packed with a preferred primer composition of 24 percent powderedzirconium, 20 percent antimony sulfide, and 56 percent barium nitrate.Table 1 shows the no fire results of the tests, and table [I s h ows t he all fire results.

TABLE I Current amps; 100% no fire Heat sink composition 60 seconds No.Tested:

50 Epoxy 0. 8 Mineral filled epoxy 1. 0 50 Alumina 1.2

TABLE II Average firing time, Current, milli- Heat sink composition ampsseconds No. Tested:

20 Epoxy 3.0 2.15 20. Mineral filled epoxy. 2 5 4. 22 20 Alumina 2. 5 5.09

it is thus readily apparent that the ignition assembly of this inventionis capable of being easily tested for operativeness by the passage of acomparatively high current therethrough without an attendant combustionof the primer charge. At the same time. however, the ignition assemblyof this invention produces complete combustion of the primer charge in acomparatively brief time upon the application thereto of a comparativelylow current. Furthermore, the excellent all fire characteristics of theignition assembly of this invention are not affected by a priorapplication of the no fire current for testing.

It is to be understood that various modifications and alterations willreadily suggest themselves to persons skilled in in the art. It isintended, therefore, that the foregoing description be considered asexemplary only, and that the scope of this invention be defined by thefollowing claims.

lclaim:

1. An electrical ignition assembly for firing an adjacent mass ofpropellant, said assembly, when loaded, exhibiting a no-firecharacteristic of at least 60 seconds duration when subjected to acurrent of approximately 0.75 ampere, and said assembly furtherexhibiting an all-fire characteristic occurring within at most 10milliseconds when subjected to a current of at least 2.5 amperes, saidignition assembly comprising:

a. an electrode;

b. electrically insulating heat sink means having a thermal conductivityin the range of about 002 gm.2cal. to about .040 gm. cal. ate-"se nsec}-Q-..

o. a bridge wire connected to said electrode, said bridge wire beingdisposed in heat exchange relationship with said heat sink means, saidbridge wire having a temperature coefficient of resistivity ofapproximately .0004 ohmcm at 20 C., and a unit resistance in the rangeof about 1.2. ohms to about 2.0 ohms; and

d. electrical ground means connected to said bridge wire.

2. The ignition assembly of claim 1, further comprising a charge of adensely packed homogenous mixture of granulated primer material disposedadjacent to said bridge wire, said primer material consistingessentially of about 18 percent to about 30 percent powdered zirconium,about 14 percent to about 26 percent antimony sulfide, and about 50percent to about percent barium nitrate. v

3. The ignition assembly of claim 2, wherein said heat sink means isformed from a material selected from the group consisting ofthermosetting epoxy resin, thermosetting mineralfilled epoxy resin, andalumina.

4. The ignition assembly of claim 2, wherein said bridge wire isNichrome.

5. The ignition assembly of claim 2, wherein said granulated charge ofprimer material is of a particle size which will pass through a 325-meshscreen.

6. The ignition assembly of claim 2, wherein said primer materialcontains about 24 percent powdered zirconium, about 20 percent antimonysulfide, and about 56 percent barium nitrate.

7. An electrical ignition assembly for firing an ejection typecartridge, said assembly exhibiting a no-fire characteristic of at least60 seconds duration when subjected to a current of approximately 0.75ampere, and said assembly further exhibiting an all-fire characteristicoccurring within at most 10 milliseconds when subjected to a current ofat least 2.5 amperes, said ignition assembly comprising:

a. an electrode for connection to a source of electric current;

b. electrically grounded means defining a sidewall of a primer chamber;

c. an electrically insulating heat sink body interposed between saidelectrode and said grounded means, said heat sink body defining a bottomwall of said primer chamber and said heat sink body being formed from amaterial selected from the group consisting of thermosetting epoxyresin, thermosetting mineral-filled epoxy resin, and alumina; and

d. a bridge wire interconnecting said electrode and said grounded means,said bridge wire extending across the bottom wall of said primer chamberin face-to-face contact with said heat sink body, said bridge wirehaving a temperature coefficient of resistivity of approximately .0004ohm-cm at 20 C. and a unit resistance in the range of about 1.2 ohms toabout 2.0 ohms.

8. The ignition assembly of claim'7, further comprising a granulatedhomogeneous mixture of primer material densely packed into said primerchamber to contact said bridge wire, said primer material consistingessentially of from about 18 percent to about 30 percent powderedzirconium, from about 14 percent to about 26 percent antimony sulfide,and from about 50 percent to about 70 percent barium nitrate.

9. The ignition assembly of claim 7, wherein said bridge wire isNichrome.

10. The ignition assembly of claim 8, wherein said granulated charge ofprimer material is of a particular size which will pass through a325-mesh screen.

11. The ignition assembly of claim 8, wherein said primer materialcontains about 24 percent powdered zirconium, about 20 percent antimonysulfide, and about 56 percent barium nitrate.

12. An electrical ignition assembly for firing an ejectiontypecartridge, said assembly, when loaded, exhibiting a nofirecharacteristic of at least 60 seconds duration when subjected to acurrent of approximately 0.75 ampere, and said assembly furtherexhibiting an all-fire characteristic occurring within at most aboutmilliseconds when subjected to a current of at least about 2.5 amperes,said ignition assembly com prising:

a. a housing of electrical conducting material for connection to anelectrical ground;

b. a lining of electrical insulating material disposed in said housing;

c. an electrode disposed in said housing and separated therefrom by saidlining, said electrode being for connection to a source of electriccurrent;

d. an electrically Calif. element disposed in said housing andelectrically connected thereto, said element defining a wall of a primerchamber;

e. an electrically insulating heat sink body interposed between saidelectrode and said element, said heat sink body defining a bottom wallof said primer chamber and said heat sink body being formed from amaterial selected from the group consisting of thermosetting epoxyresin, mineral filled therrnosetting epoxy resin, and alumina; and

f. a Nichrome bridge wire interconnecting said electrode and saidelement, said bridge wire extending across the bottom wall of saidprimerchamber in contact with said heat sink body, and said bridge wire havinga unit resistance in the range of about 1.2 ohms to about 2.0 ohms.

13. An electrical ignition assembly for firing an ejectiontypecartridge, said assembly comprising:

a. an electrode for connection to a source of electric current;

b. an element for connection to an electrical ground, said UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION 3,557 ,699 January 26, 1971Patent No. Dated Charles L. Hubbard Inventor(s) It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 6 claim 12 line 6 "Calif." should read conducting Signed andsealed this 1st day of June 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR Attesting OfficerCommissioner of Patents FORM PO-IOSO (10-69 nernnnhnr nae-IA

1. An electrical ignition assembly for firing an adjacent mass ofpropellant, said assembly, when loaded, exhibiting a no-firecharacteristic of at least 60 seconds duration when subjected to acurrent of approximately 0.75 ampere, and said assembly furtherexhibiting an all-fire characteristic occurring within at most 10milliseconds when subjected to a current of at least 2.5 amperes, saidignition assembly comprising: a. an electrode; b. electricallyinsulating heat sink means having a thermal conductivity in the range ofabout
 2. The ignition assembly of claim 1, further comprising a chargeof a densely packed homogenous mixture of granulated primer materialdisposed adjacent to said bridge wire, said primer material consistingessentially of about 18 percent to about 30 percent powdered zirconium,about 14 percent to about 26 percent antimony sulfide, and about 50percent to about 70 percent barium nitrate.
 3. The ignition assembly ofclaim 2, wherein said heat sink means is formed from a material selectedfrom the group consisting of thermosetting epoxy resin, thermosettingmineral-filled epoxy resin, and alumina.
 4. The ignition assembly ofclaim 2, wherein said bridge wire is Nichrome.
 5. The ignition assemblyof claim 2, wherein said granulated charge of primer material is of aparticle size which will pass through a 325-mesh screen.
 6. The ignitionassembly of claim 2, wherein said primer material contains about 24percent powdered zirconium, about 20 percent antimony sulfide, and about56 percent barium nitrate.
 7. An electrical ignition assembly for firingan ejection type cartridge, said assembly exhibiting a no-firecharacteristic of at leasT 60 seconds duration when subjected to acurrent of approximately 0.75 ampere, and said assembly furtherexhibiting an all-fire characteristic occurring within at most 10milliseconds when subjected to a current of at least 2.5 amperes, saidignition assembly comprising: a. an electrode for connection to a sourceof electric current; b. electrically grounded means defining a sidewallof a primer chamber; c. an electrically insulating heat sink bodyinterposed between said electrode and said grounded means, said heatsink body defining a bottom wall of said primer chamber and said heatsink body being formed from a material selected from the groupconsisting of thermosetting epoxy resin, thermosetting mineral-filledepoxy resin, and alumina; and d. a bridge wire interconnecting saidelectrode and said grounded means, said bridge wire extending across thebottom wall of said primer chamber in face-to-face contact with saidheat sink body, said bridge wire having a temperature coefficient ofresistivity of approximately .0004 ohm-cm at 20* C. and a unitresistance in the range of about 1.2 ohms to about 2.0 ohms.
 8. Theignition assembly of claim 7, further comprising a granulatedhomogeneous mixture of primer material densely packed into said primerchamber to contact said bridge wire, said primer material consistingessentially of from about 18 percent to about 30 percent powderedzirconium, from about 14 percent to about 26 percent antimony sulfide,and from about 50 percent to about 70 percent barium nitrate.
 9. Theignition assembly of claim 7, wherein said bridge wire is Nichrome. 10.The ignition assembly of claim 8, wherein said granulated charge ofprimer material is of a particular size which will pass through a325-mesh screen.
 11. The ignition assembly of claim 8, wherein saidprimer material contains about 24 percent powdered zirconium, about 20percent antimony sulfide, and about 56 percent barium nitrate.
 12. Anelectrical ignition assembly for firing an ejection-type cartridge, saidassembly, when loaded, exhibiting a no-fire characteristic of at least60 seconds duration when subjected to a current of approximately 0.75ampere, and said assembly further exhibiting an all-fire characteristicoccurring within at most about 10 milliseconds when subjected to acurrent of at least about 2.5 amperes, said ignition assemblycomprising: a. a housing of electrical conducting material forconnection to an electrical ground; b. a lining of electrical insulatingmaterial disposed in said housing; c. an electrode disposed in saidhousing and separated therefrom by said lining, said electrode being forconnection to a source of electric current; d. an electrically Calif.element disposed in said housing and electrically connected thereto,said element defining a wall of a primer chamber; e. an electricallyinsulating heat sink body interposed between said electrode and saidelement, said heat sink body defining a bottom wall of said primerchamber and said heat sink body being formed from a material selectedfrom the group consisting of thermosetting epoxy resin, mineral filledthermosetting epoxy resin, and alumina; and f. a Nichrome bridge wireinterconnecting said electrode and said element, said bridge wireextending across the bottom wall of said primer chamber in contact withsaid heat sink body, and said bridge wire having a unit resistance inthe range of about 1.2 ohms to about 2.0 ohms.
 13. An electricalignition assembly for firing an ejection-type cartridge, said assemblycomprising: a. an electrode for connection to a source of electriccurrent; b. an element for connection to an electrical ground, saidelement defining a sidewall of a primer chamber; c. an electricalinsulating heat sink body interposed between said electrodE and saidelement, said heat sink body defining a bottom wall of said primerchamber; and d. a bridge wire interconnecting said electrode and saidelement, said bridge wire extending across the bottom wall of saidprimer chamber in heat exchange contact with said heat sink body.